The present invention relates to a radiation sensitive material and a process for forming a pattern using the same.
Recently, semiconductor integrated circuits have become more integrated and LSls and VLSIs are practically available. Accompanying such integration, circuit patterns have become smaller in size, approaching submicron dimensions and even smaller. Formation of a pattern in a submicron dimension essentially requires lithography. In lithography a thin film resist is deposited on to a substrate to be processed, and is selectively exposed and developed to form a resist pattern. With this resist pattern as a mask, dry etching is conducted and then the resist is removed to obtain a required pattern. As an exposure source for lithography, ultraviolet radiation was originally used, but as circuit patterns approach submicron sizes, far ultraviolet radiation (e.g. electron beams, X rays, etc.) with short wavelengths, are used as exposure sources.
Especially for lithography using excimer lasers (248-nm wavelength KrF laser and 193-nm wavelength ArF laser), resist materials having high resolution, high sensitivity and good dry-etching resistance are required.
Many conventionally developed resists are based on phenol resin and novolak resin. These materials have aromatic rings and good dry etching resistance, but they have poor transparency at KrF wavelength and are totally opaque at ArF wavelength. Consequently they can not provide patterns sufficiently precise in submicron dimensions.
On the other hand, as a transparent resist for excimer beams, t-butyl methacrylate polymer is proposed, but this resist lacks dry etching resistance.
As a countermeasure to this, the inventors have proposed a chemical amplification type resist using alicyclic groups as a resist having dry etching resistance comparable with that of aromatic compounds and are transparent at KrF and ArF wavelength. Here alicyclic groups are adamantane, norbornane, perhydroantracene, cyclohexane, tricyclo [5.2.1.02,6 ] decane etc., and adamantyl groups are suitable (see Japanese Patent Laid-Open Publication No. 39665/1992).
But the chemical amplification type resist of alicyclic copolymer increases hydrophobicity and rigidity of the alicyclic group, which gives dry etching resistance, increases its composition ratio.
At a composition ratio which gives dry etching resistance comparable to that of phenol resin-based and novolak resin-based resists, e.g., above 50 mol % of alicyclic unit, because of high hydrophobicity and rigidity of the resists, diffusion of protonic acid as a catalyst is hindered, which results in lower amplification, smaller amounts of carboxylic acid being generated, and lower solubility to a developer of an alkaline aqueous solution.
Furthermore, these resists lack adhesiveness, and, in addition, their resist films are rigid because of inclusion of alicyclic groups. As a result, strain caused to the resist films become larger, and the resist films have a greater tendency to peel off. Accordingly stable pattern characteristics cannot be obtained. This is also a problem.
In view of these problems, an object of the present invention is to provide a radiation sensitive material for an excimer laser lithography, having good transparency and etching resistance, is highly sensitive, has good adhesion and to provide a method for forming a circuit pattern using the radiation sensitive material.
Another object of the present invention is to provide a method for forming a pattern which can produce a protective film from even a non-phenol based polymer of low polarity, and which can have stable pattern characteristics.
The above-described object of the present invention is achieved by a radiation sensitive material comprising: a copolymer expressed by a general formula 
(where Y represents alicyclic group; R1 and R2 represent CH3 or H, and at least one of R1 and R2 is H; and R3 represents alkyl group); and a substance generating an acid by application of radiation.
In the above-described radiation sensitive material, it is preferable that the copolymer includes, by 40-70 mol %, a unit structure including alicyclic groups.
The above-described object of the present invention is achieved by a radiation sensitive material comprising: a copolymer including a unit structure which is expressed by a general formula 
(where R1 represents CH3 or H); and which generates an alkali soluble group in the presence of methacrylic acid or acrylic acid, and an acid; and a substance generating an acid by application of radiation.
The above-described object of the present invention is achieved by a radiation sensitive material comprising: a terpolymer expressed by a general formula 
(where Y represents alicyclic group;
Z represents xe2x80x94C(CH3)2R4, 
R1, R2, and R3 represent CH3 or H; and R4 represents alkyl group); and a substance generating an acid by application of radiation.
Here groups which generate alkali soluble groups in the presence of acid are, an ester group, t-butyl group, tetrahydropyranyl group, xcex1,xcex1-dimethylbenzyl group, 3-oxocyclohexyl group, etc., and groups which are released in the presence of protonic acid can be used. In view of transparency with respect to excimer beams, groups without benzene rings are suitable. Thus, t-butyl group, tetrahydropyranyl group, 3-oxocyclohexyl group are more preferable.
In the above-described radiation sensitive material, it is preferable that the copolymer includes the unit structure having carboxylic acid in the range of 5-35 mol %.
The above-described object of the present invention is achieved by a radiation sensitive material comprising: a copolymer including a unit structure which is expressed by a general formula 
and which generates an alkali soluble group in the presence of methacrylic acid and an acid; and a substance generating an acid by application of radiation.
The above-described object is achieved by a radiation sensitive material comprising: a terpolymer expressed by a general formula 
(where Y represents alicyclic group; and
Z represents xe2x80x94C(CH3)2R3, 
R1 and R2 represent CH3 or H; and R3 represents alkyl group); and a substance generating an acid by application of radiation.
Here groups which generate alkali soluble groups in the presence of acid are, as ester group, t-butyl group, tetrahydropyranyl group, xcex1,xcex1-dimethylbenzyl group, 3-oxocyclohexyl group, etc., and groups which are released in the presence of protonic acid can be used. In view of transparency with respect to excimer beams, groups without benzene rings are suitable. Thus, t-butyl group, tetrahydropyranyl group, 3-oxocyclohexyl group are more preferable.
In the above-described radiation sensitive material, it is preferable that the copolymer includes the hydroxyethyl methacrylate by above 5 mol %.
The above-described object of the present invention is achieved by a radiation sensitive material comprising: a copolymer including a unit structure expressed by 
(where X1 and X2 represent xe2x80x94C(CH3)2R1, 
and R1 represents alkyl group); and a unit structure generating an alkali soluble group in the presence of an acid; and a substance generating acid by application of radiation.
The above-described object of the present invention is achieved by a radiation sensitive material comprising: a copolymer expressed by a general formula 
(where X1 and X2 represent xe2x80x94C(CH3)2R2, 
Y represents alicyclic group; R1 represent CH3 or H; and R2 represents alkyl group); and a substance generating an acid by application of radiation.
The above-described object of the present invention is achieved by a radiation sensitive material comprising: a copolymer including a unit structure expressed by 
(where X1 and X2 represent xe2x80x94C(CH3)2R1, 
and R1 represents alkyl group); and a unit structure generating an alkali soluble group in the presence of an acid; and a substance generating an acid by application of radiation.
The above-described object of the present invention is achieved by a radiation sensitive material comprising: a copolymer expressed by a general formula 
where X1 and X2 represent xe2x80x94C(CH3)2R2, 
Y represents alicyclic group; R1 represent CH3 or H; and R2 represents alkyl group); a substance generating an acid by application of radiation.
The above-described object of the present invention is achieved by a radiation sensitive material comprising: a copolymer including a unit structure expressed by a general formula 
(where at least one of X and Y is a nitrile group) and a unit structure generating an alkali soluble group; and a substance generating an acid by application of radiation.
In the above-described radiation sensitive material, it is preferable that the copolymer includes t-butyl groups.
In the above-described radiation sensitive material, it is preferable that the copolymer includes alicyclic groups.
In the above-described radiation sensitive material, it is preferable that the unit structure 
(where at least one of X and Y is nitrile group) is acrylonitrile or methacrylonitrile.
In the above-described radiation sensitive material, it is preferable that the copolymer includes the acrylonitrile or methacrylonitrile by 10-70 mol %.
The above-described object is achieved by a radiation sensitive material comprising a terpolymer expressed by a general formula 
(where X represents H or CH3;
R represents 
xe2x80x83and
R1 and R2 represent H, R3 represents 
xe2x80x83R1 represents CH3, R2 represents H, R3 represents 
xe2x80x83R1 and R2 represent CH3, R3 represents 
xe2x80x83R1, R2 and R3 represent CH3); and a substance generating an acid by application of radiation.
The above-described object is achieved by a radiation sensitive material comprising a resist containing a hydrophilic group and a hydrophobic compound.
It is preferred that the resist containing a hydrophilic group is a copolymer expressed by a general formula 
(where X represents H or CH3;
R represents 
xe2x80x83and
R1 and R2 represent H, R3 represents 
xe2x80x83R1 represents CH3, R2 represents H, R3 represents 
xe2x80x83R1 and R2 represent CH3, R3 represents 
xe2x80x83R1, R2 and R3 represent CH3)
In the above-described radiation sensitive material, the resist contains vinylphenol, which contains hydrophilic groups, in the range of 50-70 mol %.
In the above-described radiation sensitive material, the resist containing hydrophilic groups is a copolymer expressed by a general formula 
In the above-described radiation sensitive material, it is preferred that the resist contains vinylphenol, which contains hydrophilic groups, in the range of 60-80 mol %.
In the above-described radiation sensitive material, it is preferred that the hydrophobic compound is expressed by a general formula 
In the above-described radiation sensitive material, it is preferred that the hydrophobic compound is expressed by a general formula 
(where R1 and R2 represent 
or
R1 represents 
xe2x80x83R2 represents 
The above-described object of the present invention is achieved by a radiation sensitive material comprising a copolymer including itaconic anhydride which is expressed by 
and a polymer as a unit structure generates an alkali soluble group in the presence of an acid; and a substance generating an acid, upon application of radiation.
In the above-described radiation sensitive material, it is preferred that the copolymer is expressed by a general formula 
(where 1, m and n represent 0-60 mol %, 10-95 mol %, 5-50 mol % respectively; R1, R2, R3 and R4 represent H, halogen, C1-4 alkyl group, C1-4 substituted alkyl group, nitrile group, xe2x80x94(CH2)nCOOR5(n=0xe2x88x921) or xe2x80x94(CH2)nCOOR6(n=0xe2x88x921); R5 represents C1-5 alkyl group, C1-5 substituted alkyl group, alicyclic group, substituted alicyclic group, aromatic group or substituted aromatic group; and R6 represents t-butyl group, t-amyl group, dimethylbenzyl group, tetrahydropyranyl group or 3-oxocyclohexyl group).
In the above-described radiation sensitive material, it s preferred that the copolymer is expressed by 
(where 1, m and n represent 1-95 mol %, 10-95 mol % and 5-50 mol %; Z represents benzene ring, substituted benzene ring, nitrile group, xe2x80x94OR7, xe2x80x94COR7 or xe2x80x94OCOR7; R1, R2, R3 and R4 represent H, halogen, C1-4 alkyl group, C1-4 substituted alkyl group, nitrile group, xe2x80x94C(CH2)nCOOR5(n=0xe2x88x921), or xe2x80x94(CH2)nCOOR6(n=0xe2x88x921); R6 represents t-butyl group, t-amyl group, dimethylbenzyl group, tetrahydropyranyl group or 3-oxocyclohexyl group; R7 represents C1-5 alkyl group, C1-5 substituted alkyl group, alicyclic group, substituted alicyclic group, aromatic group or substituted aromatic group).
In the above-described radiation sensitive material, it is preferred that the copolymer is expressed by a general formula 
(where 1, m and n represent 0-95 mol %, 1-95 mol % and 5-50 mol % R1, R2, R3 and R4 represent H, halogen, C1-4 alkyl group, C1-4 substituted alkyl group, nitrile group, xe2x80x94(CH2)nCOOR5(n=0xe2x88x921) or xe2x80x94(CH2)nCOOR6(n=0xe2x88x921); R5 represents C1-5 alkyl group, C1-5 substituted alkyl group, alicyclic group, substituted alicyclic group, aromatic group or substituted aromatic group; and R8 represents xe2x80x94OtBu, xe2x80x94OCOOtBu or xe2x80x94COOt-Amyl).
In the above-described radiation sensitive material, the copolymer is expressed by a general formula 
(where 1, m and n represent 0-95 mol %, 1-95 mol % and 5-50 mol %; Z represents benzene ring, substituted benzene ring, nitrile group, OR7, xe2x80x94COR7 or xe2x80x94OCOR7; R1, R2, R3 and R4 represent H, halogen, C1-4 alkyl group, C1-4 substituted alkyl group, nitrile group, xe2x80x94(CH2)nCOOR5(n=0xe2x88x921) or xe2x80x94(CH2)nCOOR6(n=0xe2x88x921); and R8 represents xe2x80x94OtBu, xe2x80x94OCOOtBu, or xe2x80x94COOt-Amyl).
In the above-described radiation sensitive material, it is preferred that the copolymer includes the unit structure including itaconic anhydride by 5-50 mol %.
The above-described object of the present invention is achieved by a method for forming a pattern comprising the steps of: preparing a resist of the above-described radiation sensitive material; applying the resist to a substrate to be processed; prebaking the resist film and then selectively exposing the resist on the substrate to radiation; and post exposure baking and then developing the resist on the substrate to form the pattern.
The above-described object of the present invention is achieved by a method for forming a pattern comprising the steps of: preparing a resist of a radiation sensitive material; applying the resist to a substrate to be processed; prebaking the resist film and then selectively exposing the resist on the substrate to radiation; and post exposure baking the substrate and then developing the resist on the substrate by a developer being a mixed liquid of an organic alkaline aqueous solution and isopropyl alcohol to form the pattern.
Here the radiation sensitive material preferably comprises: a copolymer including a unit structure including alicyclic groups, e.g., adamantyl groups, norbornyl group, and a unit structure generating an alkali soluble group in the presence of an acid; and a substance generating an acid by application of radiation.
In the above-described radiation sensitive material, it is preferable that the developer contains isopropyl alcohol by 5-95 vol %.
The above-described object is achieved by a method for forming a pattern comprising the steps of: preparing a resist of a polymer containing an acrylic or methacrylic ester unit, having an alicyclic group at said acrylic or methacrylic ester unit; where said acrylic or methacrylic ester unit have a polar structure at an ester unit; coating a substrate to be processed with the resist, and prebaking the substrate to be processed; applying onto the resist a protecting film of a hydrocarbon-based polymer, which is transparent to far ultraviolet rays, and heating the same; selectively exposing radiation to the resist on the substrate to be processed; postbaking the substrate to be processed; stripping the protecting film; and developing the resist on the substrate to be processed to form a desired resist pattern, an application solvent for the hydrocarbon-based polymer of the protecting film being a non-aromatic hydrocarbon, or an aromatic hydrocarbon expressed by a general formula 
(where R represents an alkyl group with 3 or more carbon atoms).
The above-described object of the present invention is achieved by a method for forming a pattern comprising the steps of forming a resist of a radiation sensitive material coating a substrate-to-be-processed with the resist, and prebaking the substrate to be processed; applying a protecting film of a hydrocarbon polymer, which is transparent to far ultraviolet rays, and heating the same; selectively exposing radiation to the resist on the substrate to be processed, and postbaking the substrate to be processed; and stripping the protecting film, and developing the resist on the substrate to be processed to form a desired resist pattern.
In the above-described method for forming a pattern, it is preferred that an application solvent for the hydrocarbon polymer for the protecting film is limonene, 1,5-cyclooctadiene, 1-decene, t-butylcyclohexane, p-cymene or dodecylbenzene.
In the method for forming a pattern, it is preferred that the hydrocarbon polymer is an olefine polymer or a diene polymer.
In the above-described method, the substance having a polar-structure is ketone, alcohol, ether, ester, carbonic acid, an acid anhydride or any one of these substances having a part of the atoms of a polar structure.
A substance generating an acid by application of radiation used in the above-described radiation sensitive material, i.e., an acid generating substance can be provided by:
an oxazole derivative expressed by the general formula 
xe2x80x83(where R1 represents a substituted or an unsubstituted aryl group or alkenyl group; and X represents Cl or Br),
an s-triazine derivative expressed by the general formula 
xe2x80x83(where R1 represents CH3, a substituted or an unsubstituted alkyl group, or a substituted or an unsubstituted aryl or alkenyl group; and X represents Cl or Br),
an iodonium salt expressed by the general formula 
xe2x80x83(where Ar1 and Ar2 represent a substituted or an unsubstituted aromatic ring; and X represents BF6xe2x88x92, PF6xe2x88x92, AsF6xe2x88x92, SbF6xe2x88x92 or ClO4xe2x88x92, or an organic sulfonic acid anion),
a sulfonium salt expressed by the general formula 
xe2x80x83(where R1, R2and R3 represent a substituted or unsubstituted alkyl group, or an aromatic ring; X represents BF631 , PF6xe2x88x92, AsF6xe2x88x92, SbF6xe2x88x92 or ClO4, or an organic sulfonic acid anion),
a disulfone derivative expressed by the general formula
R1xe2x80x94SO2xe2x80x94SO2xe2x80x94R2
(where R1 represent a substituted aromatic ring or an alicyclic group),
an imidosulfonate derivative expressed by the general formula 
(where R1 represents a substituted or unsubstituted alkyl group or aryl group; and Z represents a substituted or unsubstituted alkylene group, alkeneylene group or aryl group), or
a diazonium salt expressed by the general formula
Ar1xe2x80x94N2+Yxe2x88x92
(where Ar1 represents a substituted or an unsubstituted aromatic ring; Y represents BF1xe2x88x92, PF6xe2x88x92, AsF6xe2x88x92, SbF6xe2x88x92 or ClO4xe2x88x92, or an organic sulfonic acid anion). But the acid generating substance is not limited to the above-described substances.
In the radiation sensitive material comprising a copolymer expressed by the following general formula 
(where Y represents alicyclic group; R1 and R2 represent CH3 or H, and at least one of R1 and R2 is H; and R3 represents alkyl group); and an acid generating material by application of radiation, either of R1 and R2 at the xcex1 positions is not a methyl group, which is bulky and very hydrophobic, but a proton, which is small-sized and less hydrophobic. Accordingly the copolymer is less hydrophobic and less rigidity. Consequently the copolymer is more compatible with and permeable to a developer, while protonic acid as a catalyst can be more diffusible. Development is therefore easier, resulting in higher sensitivity and stable patterning characteristics.
Here it is preferable that this copolymer contains a unit structure containing alicyclic groups by 40-70 mol %. In the composition with below 40 mol % of the unit structure, sufficient dry etching resistance cannot be obtained. The composition with above 70 mol % of the unit structure makes patterning difficult because of a small amount of t-butyl, a photosensitive group.
The radiation sensitive material comprising a copolymer expressed by the following general formula 
(where R1 represents CH3 or H); and an acid generating substance by application of radiation can have higher sensitivity and stable patterning characteristics because of the carboxylic acid contained in the copolymer, which is an effective hydrophilic group.
That is, because carboxylic acid is alkali soluble, the copolymer originally containing carboxylic acid becomes an alkaline aqueous solution only by substitution of the sensitive groups by a small amount of carboxylic acid. Accordingly, high sensitivity and stable patterning characteristics can be obtained.
In the radiation sensitive material comprising a terpolymer expressed by the following general formula 
(where Y represents alicyclic group;
Z represents xe2x80x94C(CH3)2R4, 
xe2x80x83R1, R2, and R3 represent CH3 or H; and R4 represents alkyl group); and a substance generating acid by application of radiation, it is very effective that the terpolymer contains carboxylic acid, which is hydrophilic, because the terpolymer contains alicyclic groups, which are very hydrophobic.
It is preferable that the terpolymer contains carboxylic acid by above 5 mol % and below 35 mol %. This is because with a carboxylic acid content of below 5 mol %, the effect is not exhibited, and with a carboxylic acid content of above 35 mol %, even non-exposed portions are solved and thus patterning is impossible.
In the radiation sensitive material comprising a copolymer including a unit structure, which is expressed by the following general formula 
and which generates alkali soluble groups in the presence of hydroxyethyl methacrylate and an acid, and an acid generating substance by application of radiation, the copolymer contains hydroxyethyl methacrylate as hydrophilic groups, whereby as in the case that the copolymer contains carboxylic acid, the copolymer has higher hydrophilicity, and thus is more compatible with a developer and is permeable, resulting in higher solubility.
In the radiation sensitive material comprising a terpolymer containing a unit structure which is expressed by the following general formula 
(where Y represents alicyclic group;
Z represents xe2x80x94C(CH3)2R4, 
xe2x80x83R1 and R2 represent CH3 or H; and R3represents alkyl group); and an acid generating substance by application of radiation, because the terpolymer contains alicyclic groups, which are very hydrophobic, it is very effective that the terpolymer contains hydroxyethyl methacrylate as a hydrophobic group.
It is preferable that the terpolymer contains hydroxyethyl methacrylate by above 5 mol % because the effect is not exhibited with a content of hydroxyethyl methacrylate below 5 mol %.
The radiation sensitive material comprising a copolymer including a unit structure expressed by the following general formula 
(where X1, and X2 represent xe2x80x94C(CH3)2R1, 
and
R1 represents alkyl group); and a unit structure generating an alkali soluble group in the presence of an acid, and an acid generating substance by application of radiation; and
the radiation sensitive material comprising a copolymer expressed by the following general formula 
(where X1 and X2 represent xe2x80x94C(CH3)2R2, 
Y represents alicyclic group; R1 represent CH3 or H; and R2 represents alkyl group); and an acid generating substance by application of radiation, both include a unit structure expressed by 
(where X1 an X 2represent xe2x80x94C(CH3)2R1, 
and
R1 represents alkyl group); whereby a larger number of sensitive groups are available per unit structure, with a result that higher sensitivity can be obtained, resulting in stable patterning characteristics.
The radiation sensitive material comprising a copolymer including a unit structure expressed by the following formula 
(where X1 an X2 represent xe2x80x94C(CH3)2R1, 
and
R1 represents alkyl group); and a unit structure generating alkali soluble groups in the presence of an acid, and an acid generating substance by application of radiation; and
the radiation sensitive material comprising a copolymer expressed by the following general formula 
xe2x80x83(where X1 and X2represent xe2x80x94C(CH3)2R2, 
xe2x80x83Y represents alicyclic group; R1 represents CH3 or H; and R2 represents alkyl group); and an acid generating substance by application of radiation, both include a unit structure expressed by 
xe2x80x83(where X1 an X2 represent xe2x80x94C(CH3)2R1, 
xe2x80x83and R1 represents alkyl group); whereby a larger number of sensitive groups is available per unit structure, and thus higher sensitivity and stable pattering characteristics can be obtained.
For more stable patterning characteristics, it is effective to improve adhesiveness. The presence of especially adamantyl groups and t-butyl groups, which are hydrocarbon, degrades adhesiveness. This is because hydrocarbon-based groups have such low polarity that there is no interaction with a substrate.
Accordingly the radiation sensitive material comprising a copolymer including a unit structure expressed by the following general formula 
(where at least one of X and Y is nitrile group), and a unit structure generating alkali soluble groups in the presence of an acid, and an acid generating substance by application of radiation can have improved adhesiveness and stable patterning characteristics because of the nitrile groups, which have high polarity.
In the case that the unit structure including nitrile groups is acrylonitrile or methacrylonitrile, its content is preferably 10-70 mol %. When its content is below 10 mol %, sufficient adhesiveness cannot be obtained, and when its content is above 70 mol %, sufficient sensitivity can not be obtained.
A radiation sensitive material comprising a polymer expressed by a general formula 
(where X represents H or CH3;
R represents 
and
xe2x80x83R1 and R2 represent H, R3 represents 
xe2x80x83R1 represents CH3, R2 represents H, R3 represents 
xe2x80x83or
R1 and R2 represent CH3, R3 represents 
xe2x80x83or
R1, R2 and R3 represents CH3); containing hydrophilic groups and highly hydrophobic groups (e.g., adamantyl, norbornyl, cyclohexyl); and a substance generating an acid by application of radiation; and a radiation sensitive material comprising a copolymer which is expressed by a general formula 
xe2x80x83(where X represents H or CH3;
R represents 
xe2x80x83and
R1 and R2 represent H, R3 represents 
xe2x80x83R1 represents CH3, R2 represents H, R3 represents 
xe2x80x83R1 and R2 represent CH3, R3 represents 
xe2x80x83R1, R2 and R3 represents CH3); or a copolymer containing hydrophilic groups and expressed by a general formula 
xe2x80x83a highly hydrophobic compound expressed by a general formula 
xe2x80x83or by a general formula 
xe2x80x83(where R1 and R2 represent 
xe2x80x83or
xe2x80x83R1 represents 
xe2x80x83R represents 
xe2x80x83are inhibited by the highly hydrophobic groups from deactivation due to contaminants (amine, etc.) in environments from the exposure to the baking, and can have high sensitivity simply by changing photosensitive groups to a small amount of alkali soluble hydrophilic groups, so that resists especially those containing highly hydrophobic groups can be stably patterned.
Here, when the hydrophilic group-content copolymer contains an excessive ratio of vinylphenol expressed by the structural formula 
the copolymer is soluble in a developer, so that even unexposed parts are solved, and patterns cannot be formed. When the vinylphenol is contained by a too small ratio, resists cannot be well stripped so that stable patterning cannot be conducted. Thus it is preferred that the hydrophilic group-content copolymer expressed by a structural formula 
(where X represents H or CH3;
R represents 
xe2x80x83and
R1 and R2 represent H, R3 represents 
xe2x80x83R1 represents CH3, R2 represents H, R3 represents 
xe2x80x83R1 and R2 represent CH3, R3 represents 
xe2x80x83or
R1, R2 and R3 represent CH3); contains vinylphenol by 50-70 mol %. It is preferred that the hydrophilic group-content copolymer expressed by the structural formula 
xe2x80x83contains vinylphenol by 60-80 mol %.
By use of the radiation sensitive material comprising a copolymer including itaconic anhydride which is expressed by 
and a polymer as a unit structure which generates an alkali soluble group in the presence of an acid, and by use of a substance generating an acid by application of radiation, resists which have good adhesion can be formed. That is, because of the strong polarity of itaconic anhydride, adhesion of resists to substrates can be greatly improved.
Itaconic anhydride itself exhibits solubility to alkali, and has to be fed to use itaconic anhydride without impairing patterning characteristics. A feed amount of itaconic anhydride is preferably 5-50 mol % although this depends on compositions and structures of the polymer. With a feed amount of 5 mol % exclusive of 5 mol %, the adhesion cannot be improved. With a feed amount exceeding 50 mol %, the resist itself becomes alkali soluble, the unexposed part of the resist is also resolved, and patterning is impossible.
Feed of such alkali soluble groups is very effective to improve resolubility of the pattern, and good patterning characteristics can be obtained.
The copolymer containing itaconic anhydride has specific structures expressed by the general formula 
(where 1, m and n represent 0-60 mol %, 10-95 mol %, 5-50 mol % respectively; R1, R2, R3 and R4 represent H, halogen, C1-4 alkyl group, C1-4 substituted alkyl group, nitrile group, xe2x80x94(CH2)nCOOR5(n=0xe2x88x921) or xe2x80x94(CH2)nCOOR6(n=0xe2x88x921); R5 represents C1-5 alkyl group, C1-5 substituted alkyl group, alicyclic group, substituted alicyclic group, aromatic group or substituted aromatic group; and R6 represents t-butyl group, t-amyl group, dimethylbenzyl group, tetrahydropyranyl group or 3-oxocyclohexyl group), 
(where 1, m and n represent 1-95 mol %, 10-95 mol % and 5-50 mol %; Z represents benzene ring, substituted benzene ring, nitrile group, xe2x80x94OR7, xe2x80x94COR7 or xe2x80x94OCOR7; R1, R2, R3 and R4 represent H, halogen, C1-4 alkyl group, C1-4 substituted alkyl group, nitrile group, xe2x88x92C(CH2)nCOOR5(n=0xe2x88x921), or xe2x80x94(CH2)nCOOR6(n=0xe2x88x921); R6 represents t-butyl group, t-amyl group, dimethylbenzyl group, tetrahydropyranyl group or 3-oxocyclohexyl group; R7 represents a C1-5 alkyl group, C1-5 substituted alkyl group, alicyclic group, substituted alicyclic group, aromatic group or substituted aromatic group), 
(where 1, m and n represent 0-95 mol %, 1-95 mol % and 5-50 mol %; Z represents benzene ring, substituted benzene ring, nitrile group, OR7, xe2x80x94COR7 or xe2x80x94OCOR7; R1, R21 R3 and R4 represent H, halogen, C1-4 alkyl group, C1-4 substituted alkyl group, nitrile group, xe2x80x94(CH2)nCOOR5(n=0xe2x88x921) or xe2x80x94(CH2)nCOOR6(n=0xe2x88x921); and R8 represents xe2x80x94OtBu, xe2x80x94OCOOtBu, or xe2x80x94COOt-Amyl), 
(where 1, m and n represent 0-95 mol %, 1-95 mol % and 5-50 mol %; Z represents benzene ring, substituted benzene ring, nitrile group, OR7, xe2x80x94COR7 or xe2x80x94OCOR7; R1, R2, R3 and R4 represent H, halogen, C1-4 alkyl group, C1-4 substituted alkyl group, nitrile group, xe2x80x94(CH2)nCOOR5(n=0xe2x88x921) or xe2x80x94(CH2)nCOOR6(n=0xe2x88x921); and R8 represents xe2x80x94OtBu, xe2x80x94OCOOtBu, or xe2x80x94COOt-Amyl), or other structures.
Here the so-called alicyclic group is adamantyl, norbornyl, cyclohexyl, a substance partially having tricyclo[5.2.1.0] decane skeleton or others, but is not limited to them.
Groups generating alkali soluble groups in the presence of an acid are t-butyl ester, t-amyl ester, t-butyl ether, t-BOC, tetrahydropyranyl, tetrahydropyranyl ether, 3-oxocyclohexyl ester or dimethylbenzyl ester, but is not limited to them.
That is, a resist is formed of the above-described radiation sensitive material, and the resist is applied onto a substrate to be processed, prebaked, exposed, postbaked and developed, and is subjected to other treatments, whereby a submicron dimension pattern can be formed stably.
To obtain more stable patterning characteristics, it is necessary to improve developers. Chemical amplifying resists have the intrinsic problem that protonic acid becomes inactive on the surface layers due to contamination by environmental amine, etc. Consequently solubility differences take place between the surface and inner layers, which is a serious factor that hinders stable patterning. Especially adamantyl groups, t-butyl groups, etc., Hydrocarbons, which are very hydrophobic, especially adamantyl groups, t-butyl groups, etc., are effective to hinder dissolution in developers, and are very effective at making the surface insoluble.
Accordingly, a mixed liquid of an organic alkaline aqueous solution and isopropyl alcohol is used as a developer, whereby solubility is much improved and smaller solubility differences between the surface and inner layers can be obtained, so allowing stable patterning. Isopropyl alcohol is the most effective alcohol to be added as methanol and ethanol cause cracks, and peelings are found. The use of this liquid mixture developer raised the sensitivity by one or more places and reduced strain caused upon development, so that the adhesiveness was much improved.
It is preferable that the developer contains isopropyl alcohol by 5-95 volt. This is because content of isopropyl alcohol by below 5 mol % does not improve the sensitivity, and content above 95 mol % easily causes cracks and crazes.
A polymer containing an acrylic or methacrylic ester unit, each having an alicyclic group and a polar structure at an ester unit, has such a high base polymer polarity that the very high hydrophobicity due to the alicyclic group can be lowered. As a result, polarity differences occur between the polymer and the hydrocarbon-based protecting film, and the protecting film can be applied without resolving the resist film, whereby a pattern of a desired size can be formed.
Examples of substances having high polarity structures are ketone, alcohol, ether, ester, carbonic acid, an acid anhydride, or any one of these substances having some of the atoms of their polar structure replaced by sulfur, nitrogen or halogen atoms, but is not limited to them.
The ratio of feed of the materials having polar structures must be at least 1-50 mol %, preferably 20% or greater.
Although the resist containing itaconic anhydride contains highly hydrophobic hydrocarbon groups, the resist permits hydrocarbon-based polymers, which have not been conventionally applied to the resist as a protecting film because of the high polarity of itaconic anhydride.
Formation of such protecting films on the resist can avoid the problem of PED (Post Exposure Delay), which is characteristic of chemical width increment resists.
A high molecular weight hydrocarbon-based solvent is used as the solvent for application of the protecting film, so that the protecting film can be applied with higher accuracy. Application solvents with too low a boiling point make it difficult to uniformly apply the protecting film on wafers. Preferably solvents have boiling points above 100xc2x0 C. are used. Examples of preferable solvents are limonene, 1,5-cyclooctadiene, 1-decene, t-butylcyclohexane, p-cymene, dodecylbenzene, etc.
The hydrocarbon polymer is, for example, olefine, diene, etc. but is not limited to them as long as the hydrocarbon polymers are transparent to exposure wavelengths and are soluble in the above-mentioned solvent.
The alicyclic group is, for example, cyclohexane, norbornane, adamantyl, and substances having a tricyclo [5.2.1.0].decane skeleton, but is not limited to them.